1. Field of the Invention
The present invention relates to a liquid ejecting recording process, and more particularly, to a liquid ejecting recording process which comprises ejecting liquid, projecting a liquid droplet, and recording.
2. Description of the Prior Art
The non-impact recording system has become of interest in recent years since the system is substantially free from noise during recording. Among the non-impact recording system, the so-called ink jet recording process (the liquid ejecting recording process) is recognized as a very useful recording system, since the recording can be carried out at high speed and made on plain paper without any particular fixing treatment. Heretofore, various ink jet recording methods have been proposed. Some are practicably used and some are still under development.
Among ink jet recording methods, the method disclosed in Deutsche Offenlengungsschrift (DOLS) Nr. 2843064 has a feature that heat energy is applied to a liquid to eject liquid droplets, that is, heat energy is utilized as an energy for forming liquid droplets. This feature is quite different from features of conventional ink jet recording methods.
According to the method as disclosed in the abovementioned patent applications, when a liquid is actuated by heat energy, the liquid is subjected to a state change including a rapid increase in volume and the resulting actuating force serves to eject liquid droplets from an orifice at the tip of the recording and the ejected droplets are deposited onto a record receiving member.
The liquid ejecting recording process disclosed in DOLS Nr. 2843064 has such advantages that it is not only very effectively applicable to the so-called "drop-on-demand recording system", but it may have the recording head portion arranged in the form of high density multi-orifice in full breadth of the recording pages. Therefore, it is a feature of the present process that images which are excellent in resolution and of high quality are obtained.
As mentioned above, said liquid ejecting recording process has excellent advantages. However, it is necessary that the life (durability) on repeated use of the recording head is enhanced in order to record images of excellent resolution and high quality at a higher speed for a long time, or to increase greatly the life of the apparatus.
The life of the recording head employed in the foregoing recording process is mainly determined by the life of an electrothermal transducer. For example, the recording head employed in the foregoing recording process has such a structure as shown in FIGS. 1A and 1B. In general, an electrothermal transducer 102 contacts a liquid introduced in the direction of arrow A at a heating surface 109 (an energy applying surface) in a heat acting portion 107 (a liquid droplet forming energy actuating portion), and the generated heat energy (a liquid droplet forming energy) is effectively and efficiently applied to the liquid present in heat acting portion 107.
When water is used as a liquid medium for the recording liquid, an upper layer 112 is disposed at least on a resistive heater layer 111 at a heat generating portion 108 so as to prevent shortcircuiting through the recording liquid between electrodes 113 and 114 and protect a resistive heater layer 111 from attack by the recording liquid or thermal oxidation. When the liquid medium is not water, the above situation may be changed.
In the process using such recording head, the principle forming a liquid droplet of the recording liquid is as follows: when electric current is conducted to said electrothermal transducer, the resulting heat energy (a liquid droplet forming energy) is applied to a recording liquid in heat acting portion 107 and thereby a state change of the recording liquid accompanied by a rapid increase in volume (i.e. a change that the recording liquid in heat acting portion 107 is converted to a gaseous state in a very short time such as less than micro-second) is caused, and a bubble is generated and grown in a moment in the heat acting portion 107. Then, when said electric current is off, the bubble is rapidly shrunk and disappears in a moment. This shrinking and disappearing speed is almost the same as or a little slower than the speed of bubble generation and growing, and anyhow it is very fast.
The present inventors have found that in this repeating of generation, growing, shrinking and disappearing, particularly, the latter part, i.e. the shrinking and disappearing of bubble, is an important factor determining the life of the electrothermal transducer.
The process of shrinking and disappearing of a bubble proceeds at a remarkable high speed so that the resulting shock wave directly attacks the heating surface 109, and therefore, upon each liquid droplet ejection the heating surface 109 is attacked by the shock wave resulting in corrosion or destruction of the heating surface due to the shock wave. In particular, the higher the application frequency (driving frequency) of the input pulse signal to drive electrothermal transducer 102, that is, the higher the frequency of liquid droplet formation for high speed recording and the higher the level of the input pulse signal, the larger the attack of the shock wave to the heating surface 109, and this is a fundamental cause of shortening the life of electrothermal transducer 102.